The proposed experiments are designed to study the effects of early experience upon the development and functioning of the visual system, from both a behavioral and a physiological point of view. In these experiments, kittens are raised in darkness except for a brief period of specified visual experience each day, such as viewing the environment through goggles containing prisms that produce a relative rotation of the visual fields seen by the two eyes. Then, upon reaching 6 to 8 months of age, the kittens are tested behaviorally to determine the effects of this experience upon selected aspects of visual perception (e.g. discriminating the orientations of line stimuli). Semichronic electrophysiological recording sessions are interspersed with the behavioral test sessions; during these recording experiments the binocularity, receptive field properties, and orientation specificity of individual visual cortical neurons are determined. There are two principal goals: first, to study plasticity in visual development; and second, to clarify the role played by the response characteristics of visual cortical neurons in behavioral perception.